1. Field of the Invention
The present invention relates to a method for producing a liquid crystal display, a liquid crystal aligning agent, a liquid crystal aligning film, and a liquid crystal device.
2. Discussion of the Background
A horizontal alignment-mode liquid crystal display that utilizes a nematic liquid crystal having positive dielectric anisotropy (e.g., twisted nematic (TN)-mode or super twisted nematic (STN)-mode liquid crystal display), and a vertical alignment (VA)-mode liquid crystal display (homeotropic alignment mode) that utilizes a nematic liquid crystal having negative dielectric anisotropy have been known. An in-plane switching liquid crystal display having a configuration in which an electrode is formed on only one of a pair of substrates disposed opposite to each other, and an electric field is applied parallel to the substrate has also been known. Note that the term “in-plane switching liquid crystal display” used herein includes an in-plane switching (IPS)-mode liquid crystal display, a fringe field switching (FFS)-mode liquid crystal display, and a liquid crystal display that utilizes a principle similar to those of these liquid crystal displays.
The in-plane switching liquid crystal display has a wide viewing angle, and achieves high-quality display as compared with the horizontal alignment-mode liquid crystal display, the VA-mode liquid crystal display, and the like. The in-plane switching liquid crystal display achieves a wide viewing angle and high contrast when the pretilt angle is small. Therefore, when implementing the in-plane switching liquid crystal display, it is desirable that the pretilt angle be small in a state in which an electric field is not applied.
A liquid crystal display is designed so that a liquid crystal alignment film is formed on the surface of a substrate in order to align the liquid crystal molecules in a given direction relative to the surface of the substrate. In recent years, a photoalignment method that implements a liquid crystal alignment capability by applying polarized or unpolarized radiation to a radiation-sensitive organic thin film formed on the surface of the substrate has been proposed to replace a rubbing method that rubs the surface of an organic film surface formed on the surface of the substrate in one direction using a fabric material such as rayon (see Japanese Patent Application Publication (KOKAI) No. 2003-307736, Japanese Patent Application Publication (KOKAI) No. 2004-163646, Japanese Patent Application Publication (KOKAI) No. 2002-250924, Japanese Patent Application Publication (KOKAI) No. 2004-83810, and Japanese Patent Application Publication (KOKAI) No. 2010-217868). A uniform liquid crystal alignment film can be formed using the photoalignment method while suppressing formation of dust and generation of static electricity during the process. Moreover, a liquid crystal alignment capability can be provided to only an arbitrary area of the organic thin film by applying radiation through an appropriate photomask, and a plurality of areas that differ in liquid crystal alignment direction can be provided to a single organic thin film by utilizing a method that applies radiation a plurality of times while changing the irradiation direction or the direction of the polarization axis, or combining such a method with a method that utilizes a photomask. In principle, a liquid crystal alignment film formed by the photoalignment method can achieve a pretilt angle of 0° by applying polarized radiation in the direction normal (vertical) to the surface of the substrate, for example. This makes it possible to produce a high-quality display.
It is desirable to produce an in-plane switching liquid crystal display using the photoalignment method in view of the above advantages. However, since an in-plane switching liquid crystal display produced using the photoalignment method may show a residual image and a burn-in phenomenon, it is important to suppress a residual image and a burn-in phenomenon. In particular, a difference in brightness due to a temporal change in alignment state is observed as a burn-in phenomenon. Since a liquid crystal display can achieve high-brightness display, and may be used outdoors in the daytime, the liquid crystal display and the liquid crystal alignment film included in the liquid crystal display may be exposed to intense UV light for a long time. Therefore, it has become important to improve the UV resistance of the liquid crystal alignment film.
The in-plane switching liquid crystal display that achieves high-quality display irrespective of the viewing angle has been widely used as a medical display, a large-scale display, a small display for portable terminals, and the like. In recent years, development of a display that can achieve high-quality display irrespective of the viewing angle, and can be mass-produced has been strongly desired along with the development of new media such as a tablet PC and a smartphone.
In view of the above situation, it has been desired to provide a liquid crystal aligning agent that can form a liquid crystal alignment film that is used for the in-plane switching liquid crystal display, and ensures that the above advantageous effects due to the photoalignment method are sufficiently achieved, a residual image and a burn-in phenomenon are sufficiently suppressed, and a decrease in voltage holding ratio rarely occurs even when the liquid crystal display (liquid crystal alignment film) is exposed to intense UV light.